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A counterexample is an example that disproves a mathematical conjecture or a purported theorem. For example, the Peterson graph is a counterexample to many seemingly plausible conjectures in Graph Theory.
5
votes
0
answers
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Can a manifold be triangulated with minimal surfaces
It is a fact stated as an exercise in chapter 9 of Lee's book "Riemannian Geometry" that any compact 2D manifold can be triangulated by geodesic triangles. Can one triangulate any compact Riemannian m …
7
votes
1
answer
615
views
Composition of power series is power series?
$\DeclareMathOperator\dom{dom}$Sorry to bother the community again with these type of questions about power series, I am ready to delete the question if it is not suitable.
Definition: I say a functio …
1
vote
1
answer
502
views
Algebraic independence in polynomial rings over $\mathbb{Z}_n$
Let $R<S$ be an extension of commutative rings with identities (i.e. $R$ is a subring of $S$). We say $s_1,s_2,...,s_k$ are algebraically independent over $R$ iff there is no polynomial $f\in R[x_1,. …
3
votes
1
answer
130
views
If $\min(\alpha,F)$ has only one root in $E$, must $\min(p(\alpha),F)$ have only one root in...
Let $F\subseteq E$ be an algebraic field extension. Let $\alpha\in E$ be such that $\min(\alpha,F)$ has only one root in $E$ (which will be $\alpha$). Is it true that for any $p(x)\in F[x]$ we must ha …
3
votes
1
answer
180
views
Is the continuous dual of a topological chain complex chain equivalent to the algebraic dual?
I apologize in advance if this is a naive question.
Def: A topological chain complex is a chain complex of topological $\mathbb{R}$-vector spaces such that the boundary maps are continuous.
Let $C$ …
0
votes
1
answer
96
views
Must a surjective infinitesmal isometry between simply connected spaces be injective? [duplicate]
Let $f:M\rightarrow N$ be a smooth map between two simply connected Riemannian manifolds of the same dimension. It is also given that for every $x\in M$ we have that $Df|_x:T_xM\rightarrow T_{f(x)}N$ …
2
votes
1
answer
185
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Local equality of functions implies global equality?
The following question arised in my research, and I was unable to settle it after playing with it for sometime. Let $\{a^k_i\}_{i\geq 1}$ (for $k\in \{1,2,3,4\}$) be four sequences of real numbers. F …